To "American" it by what would be a general BJCP style is to make it hoppier. You said you wanted to stay malty though. Balance is important! So some more unfermentable sugars which would give it malt characteristics. Low Lovibond crystal (aka carmel) malt would do that without too much extra color added. Under 60 and more likely about a 15 or 20 L. Switching to Cascade (shudder, I hate cascade hops) would make most any judge think American! Adding a couple ounces at 5 minutes near the end would make it very flowery and give it a lot of typical American hop aroma.

I made a Wee Heavy recently, and used some Scotch soaked oak chips in it. Not my favorite final product, but the first 5 gallons are already gone! I have a 4 gallon carboy waiting to be kegged yet. Letting that one age a while longer with the oak and scotch. It was not intended to be "American". Just saying, it's easy to modify a recipe a little along the way to make something non-standard!